Your dirt bike is pretty tough, but it won’t run for very long without engine oil.
A dirt bike will start without engine oil, however doing so risks severe engine damage to bearings, piston, and cylinder.
In this post, you’ll learn why engine oil is so important. I’ll also cover the top 3 reasons a dirt bike won’t start and what you can do to fix it.
Engine Oil
A 2 stroke or four-stroke dirt bike engine will start without oil but doing so will cause significant engine damage. Some higher-end bikes may be fitted with a low oil level fail-safe sensor, which prevents engine starting but generally a bike will start with low or even no oil.
Oil is the one fluid your bike can’t live without. As your engine operates, it creates friction which causes heat. If engine heat isn’t managed, it simply becomes so great that the metal components like bearings, rings, piston, and cylinder fuse together and the engine seizes. And a seized engine generally isn’t worth fixing.
Oil is the main player when it comes to managing engine heat. Fresh oil is important, it not only helps cool components, but also coats components like bearings in oil causing them ride on a film of oil instead of metal on metal. Without oil, the metal-on-metal friction would kill your motor within minutes or faster at higher RPM.
But oil does even more good work, detergents in the oil help keep your engine internals free from contaminates associated with combustion. Detergents break down harmful acids and carbon deposits that naturally occor in all internal combustion motors.
Old Oil
Engine oil is the one fluid you’ve got to get right. The type, quality, and quantity are important. Using the recommended oil in your motor is the best advice, as your engine maker has likely tested your engine to destruction and determined the optimum grade oil for performance and longevity.
Old oil loses its ability to cool. It becomes diluted by gas and overcome by harmful acids. Changing your engine oil regularly is the one maintenance job that pays off big-time. Oil is cheap. An engine rebuild isn’t.
Although you should opt for the manufacturer’s spec oil, you should also consider the ambient temperatures your bike will operate. More extreme climates will require a different grade of oil.
Colder climates require a thinner winter-grade oil and a super hot climate a higher grade.
Oil Quantity
And finally, quantity, having too little oil in the motor causes the oil to overheat and reduce its ability to work. Almost as bad is having too much oil in the engine, which is a very common occurrence.
Too much oil reduces crankcase splash, and the oil can become aerated, which has the effect of reducing oil coverage on crucial components.
2 Stroke & 4 Stroke Engines
Dirt bike engines come in two flavors, two-stroke and four-stroke. Both need oil. A four-stroke uses engine oil the same way as a car, but in addition, a four-stroke dirt bike engine oil works even harder as the engine oil also lubricates the transmission.
A two stroke does engine lubrication a little differently, it mixes specially formulated two-stroke oil with the gas to manage engine friction. The ratios are exact and must be respected. Mixing too much or too little oil can cause some serious engine damage.
An incorrect two-stroke mix can also prevent your engine from starting. Too much oil can foul the plug, too little, and the engine risks damage.
Two-stroke dirt bike transmissions are lubricated separately using transmission oil.
Checking Dirt Bike Engine Oil
Checking and topping up the oil is a one-minute job. You’ll need a clean rag, funnel, and some top-up oil. Some dirt bikes make this really easy.
They fit a sight glass on the crankcase cover. The oil level should be at the very top of the glass.
The following guide is for a regular dipstick style:
- Park the bike on level ground
- Allow engine cool if running
- Locate dipstick
- Clean around dipstick
- Remove stick and clean
- Reseat dipstick
- A reading in the hatched area is ok, but at the top mark (Full) is best
Top Dirt Bike No Start Reasons
There may be many reasons why your dirt bike won’t start, but oil generally won’t be the cause unless your engine has seized. For this guide, we’ll assume your engine isn’t seized. First off, you’ll need oil in the motor. Your engine not starting might be a blessing in disguise, if you know what I mean.
Here we’ll list all the easy-to-check stuff before getting into the top three causes of dirt bike no starts.
Check the following:
- Choke “On” or primed
- Kill switch set to “Run” or ignition on (if fitted)
- Fresh gas in tank and petcock “On” – stale gas a very common cause of no starts especially if the bike has been sitting for more than a month
- Spark plug wire on firmly
- Air filter clean, dry and air way clear
The top 3 reasons a dirt bike won’t start include:
- Old gas in the tank
- Gummed carburetor
- Contaminated spark plug
1 Old Gas
Bad gas is a persistent issue, and that’s because dirt bikes are left idle more than not. Old gas goes stale, regular after three months, and blended after about a month.
How to fix it?
If you suspect your gas is old, go ahead and drain the gas tank, removing the fuel line and placing it in a suitable catch container is the fastest way.
You’ll need to drain the carburetor gas bowl too (fuel-injected bikes won’t need to do this)
Now fill with fresh gas and crank her over, I advise all my customers to use a gas stabilizer in their gas tank. Job done!
2 Gummed Carburetor
This is a little more work. It, too, is caused by old gas, but the difference here is the gas has evaporated and left behind a sticky gum that blocks up the pilot and main jets. The jets feed gas to the engine, and with these guys blocked, you’re going nowhere.
How to fix it?
You’ll need to remove the carburetor, dismantle and clean it thoroughly, either in an ultrasonic tank or using a carb cleaner.
You’ll notice the difference with a clean carb, but you will likely need to tune the AFR afterward.
3 Contaminated Spark Plug
A fouled plug is common too, as you know too much gas can flood the plug. A wet or oily plug won’t generate a spark strong enough to ignite the fuel mix.
How to fix it ?
To dry out a wet motor we have three options. 1 Try waiting twenty minutes, the fuel will usually simply evaporate.
2 And if you can’t wait, try cranking over the motor slowly with choke-off and throttle held wide open, this helps dry out the cylinder.
Then attempt to start in the usual way.
3 Remove the plug, clean, and check the plug gap as per spec. A closed gap won’t spark.
A constantly oily plug or flooding is a symptom of an underlying engine issue.
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- About the Author
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John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.